Angina is chest pain that occurs when the heart muscle is not getting enough oxygen. It is commonly described as a crushing or squeezing pain in the chest. Oxygen is carried by red blood cells and delivered to the heart muscle via the coronary arteries. Over the years, the insides of the coronary arteries can narrow. The most common cause is a build-up of plaque. As the insides of the arteries become narrow, blood flow is reduced, and your heart has to work harder to get the oxygen it needs.